Jose Mourinho said his team paid for being too passive in the fiinal 20 minutes at West Brom.
The Chelsea boss said they sat too deep, happy to absorb pressure rather than dictate - giving the home side the encouragement they needed to grab an unlikely point.
"For 60 minutes, we were very comfortable in the game, maybe too comfortable," Mourinho said.
"Maybe you have to kill the game and we had lots of situations to kill the game and once more we didn't.
"They [West Brom] had a good reaction and my defenders were not strong enough to get out with our defensive line far from our goal.
"We were not strong enough to get out in the last 10 minutes or maybe my defenders were waiting comfortably in the box for the game to end."
The Chelsea boss added: "I feel every game is difficult because every team has different objectives and they need points.
"West Brom fought a lot for it until the end and they were better than us for the last 20 minutes."